Fluidized silica gel catalysts containing vanadium pentoxide and oxides of metals of group iii-b and iv-a



Unit I States FLUIDIZED SILICA GEL CATALYSTS CONTAIN ING VANADIUMPENTOXIDE AND OXIDES OF METALS OF GROUP III-B AND IV-A No Drawing.Application November 18, 1954, Serial No. 469,842

8 Claims. (Cl. 252-456) This invention relates to catalysts for thevapor phase catalytic oxidation of hydrocarbons, especially useful inoxidizing naphthalene to produce a converter product relatively rich in1,4-naphthoquinone, and to the process of preparing such catalysts.Throughout the remainder of the specification and claims, it will beunderstood that the term naphthoquinone is limited to the 1,4-isomer, asthe other theoretically existing isomers are not obtained by the vaporphase oxidation of naphthalene. More particularly, the invention relatesto a fluidized catalyst for oxidizing naphthalene to naphthoquinone.

In the past, the catalytic vapor phase oxidation of naphthalene hasachieved enormous commercial success for the production of phthalicanhydride. Originally, the practical processes involved converters usingfixed beds of catalysts. More recently, fluidized catalyst plants havebeen designed for the production of phthalic anhydride.

In the production of phthalic anhydride, every effort is made to reactall of the naphthalene and to produce as little naphthoquinone aspossible. Unreacted naphthalene in the converter product presents apurification problem and also results in lowered yields. Similarly,naphthoquinone which tends to form colored impurities, is kept tominimum.

Recently, there has been developed a process, described and claimed inthe co-pending application of Lecher and Whitehouse, Serial No. 236,844,filed July 14, 1951, now U. S. Letters Patent 2,652,408, for theproduction of anthraquinones using as a raw material converter productscontaining naphthoquinone.

Pure naphthoquinone has been, of course, of a laboratory curiosity andcannot be produced on a large scale at moderate cost. Attempts have beenmade to produce a converter product which has a relatively highercontent of naphthoquinone. These attempts have not been successful withfixed bed catalytic process. However, we have found that with fluidizedcatalysts it is possible to produce a converter product having a muchhigher naphthoquinone content by following certain definite procedures.More specifically, we have foundjthatce'rtain silica gel catalysts of aparticle'size suitable for fluidization, having vanadium pentoxide asits major catalytic component, stabilized with an alkali metal salt andpromoted with an oxide of a metal from group III-B orIV-A of theperiodicsystem, are especially valuable, not only for oxidizingnaphthalene to naphthoquinone, but also for oxidizing hydrocarbons ingeneral. I

l Ihe'first essential of the process usingthe catalyst of the presentinvention isto produce a converter product which contains substantialamounts of unreacted naphthalene. This result goes directly contrary tothe optimum procedures for producing phthalic anhydride. We have foundthat not only is it possible to increase markedly the naphthoquinonecontent of the converter product produced but this increase is obtainedWithout more or less any substantial decrease in the total yield ofoxid-ation reacted naphthalene also lncreases product produced, based onnaphthalene which has actually been oxidized. Since the procedure forobtaining anthraquinone described in the Lecher and Whitehouse patentreferred to above, automatically as a part of the process recoversunreacted naphthalene and phthalic anhydride, We have the unusualsituation of an improved process of producing one constituent withoutadversely affecting the production of the other constituent. In order toproduce a converter product containing unreacted naphthalene, we havefound it necessary to operate at lower temperatures than can be used foreffective production of phthalic anhydride and higher naphthaleneloadings. The two factors of temperature and naphthalene loading aremutually dependent. Higher temperatures and higher naphthalene loadingsproduce more unreacted naphthalene. At lower temperatures, a lowerloading is used. In general, the temperatures run from a minimum of 250C. to a maximum of about 425 C. The naphthalene loadings for optimumresults fall within the range from 0.5% to 2% over .the temperaturerange of 300-425 C. Slightly lower loadings may be used at still lowertemperatures. The naphthalene loadings are referred to throughout thespecification and claims in the conventional manner for modern vaporphase catalytic oxidation, namely, in mol percent, that is to say, molsof naphthalene per hundred mols of air.

Contact time is an important factor and strangely enough, it is muchlonger than in the case of the produc tion of-phthalic anhydride wherein the past, contact times of less than 4 seconds have been recommended.In spite of the fact that the present invention depends on a much lowerdegree of oxidation, which would ordinarily dictate much shorter contacttimes, we have found that just the opposite is true and that contacttimes should be 8 seconds or more. Of course, the contact time is not anisolated variable and depends to some extent on temperature. The lowerlimit of 8 seconds can only be used at the top of the temperature range.At lower temperatures contact times will preferably be longer and mayreach 50 seconds.

As far as the operation of the fluidized catalyst con-v verter isconcerned, it is an advantage of the present in vention that standardprocedures may be used and no new techniques are required. Depending onthe physical nature of the fluidized catalyst used, gas velocities from/2't0 3 feet per second are employed, which is in accordance with goodpractice. Optimum results are usually obtained with gas velocities offrom 1 to 2 feet per second. I

The process of oxidizing naphthalene to naphthoquinone may be carriedout with ordinary vanadium oxide catalyst such as have been employed forthe production of phthalic anhydride. However, we have found thatcertain promoted vanadium oxide catalyst prepared in a particular waygive optimum amounts of naphthoquinone. These special catalysts are,indeed, excellent catalysts for the oxidation of hydrocarbons ingeneral. The preferred catalysts are promoted by oxides of metals ofgroups IlL-B and IV-A of the periodic system.

In general, it is possible, by use of the catalysts of the presentinvention, to produce a converter product having a naphthoquinone tophthalic anhydrideratio of from 1:1 to about 1:20. As the naphthoquinoneto phthalicanhydride ratio is increased, the amount ofunand a compromiseis usually struck between reasonable naphthoquinone content and adequateyields. The compromise is dictated largely by economic factors, one ofwhich is the market for phthalic acid because, when the product of thepresent invention is used to prepare anthraquinones, the

Patented Oct. 15, 1957.

phthalic anhydride is recovered as phthalic acid. When there is a gooddemand for phthalic acid, therefore, the naphthoquinone content of theproduct should not be increased to the point where it would seriouslyrestrict output. On the other hand, where the market for phthalic acidis not so great or where its price is sufficiently lower than that ofphthalic anhydride so that transformation into the latter is uneconomic,it pays to strive for maximum naphthoquinone content even at some lossof phthalic anhydride. It is an advantage of the present invention thatit is very flexible and the best compromise can be chosen to suit theeconomic conditions.

It is possible to produce naphthoquinone using the catalysts of thepresent invention in a manner so that it is not necessary to regeneratethe catalyst at frequent intervals. This, however,

part of the bed, gradually zone. Catalyst regeneration where theeconomics of the According to the present invention, catalysts can beprepared which are highly effective in the oxidation of hydrocarbons,and specifically in the oxidation of naphthalene to produce a converterpresent invention, the alkali salts are kept in the catalyst by avoidingwashing steps. We do not know exactly why the catalystsof our inventionmust have the alkali salt stabilizer and do not wish to be bound by anytheory thereon.

However, thorium naphthalene are obtained. 7 The present invention is vnot limited in its broader aspects to catalysts in which the silica gelis produced at any particular pH. In more specific aspects, however, apreferred modification involves catalysts in which silica gel isprecipitated at a pH not exceeding 8 and, more especially, not exceeding6. The invention includes the new process of preparing such catalysts.It is not known why the catalysts in which the gel is prepared on theacid side give better results in the oxidation of naphthalene to aconverter product rich in naphthoquinone and it is not intended to limitthe invention to any theory of why these preferred catalysts giveimproved results.

The invention will be described in greater detail in conjunction withthe following specific examples. The parts shown are by weight.

Example I The aluminum oxideV2O5 catalyst was prepared by adding to 31.5lbs. of 30 B. potassium silicate solution in 86 lbs. of water, 30.5 lbs.of 17% sulfuric acid, the addition being rapid and with constantstirring. The pH was then adjusted to 8.0 by the addition ofconcentrated ammonium hydroxide, and 8.55 lbs. of ammonium metavanadatedissolved in 26.5 lbs. of water, containing 350 cc. of ammoniumhydroxide, was then added to the slurry. Then 342 grams of potassiumaluminum sulfate and 2.1 liters of hot water also were introduced andthe slurry concentrated by evaporation to about half its originalvolume. A gel formed, which was dried at C., calcined at 45 0 C. andground to fluidized catalyst fineness.

Example 2 The procedure of Example 1 was followed but the potassiumaluminum sulfate was replaced with 135 grams of zirconium nitrate in 1.5liters of water.

Example 3 B. potassium silicate solution and was mixed with 57 parts ofammoand 920 parts of 17% sulfuric acid, and the pH adjusted to 6.0 bymeans of concentrated ammonium hydroxide. The temperature was thenraised to about 65 C. and 9 parts of zirconium nitrate dissolved in 100parts of water added. The slurry was aged at the same temperature andthen the temperature raised to evaporate the water until the volume wasreduced by from /2 to /3. The orange colored slurry was then dried at100 C., calcined at 450 C. and ground to fluidized catalyst fineness.

953 parts of 30 2600 parts of water nium metavanadate Example 4 953parts of 30 B. potassium silicate was dissolved in 2600 ml. water,placed in an enameled pail and stirred. 57 g. of powdered ammoniummetavanadate was added slowly and allowed to dissolve. 920 g. of 17%sulfuric acid was then added and the gel brought to pH 8 with ammonia.The temperature of the thick gel was brought to 65 C. and a solution of13.5 g. thorium nitrate in water added. The gel was stirred at 65 C. forone hour. Then the temperature was raised to 95-100 C. and the slurryevaporated with stirring to one third of its original volume. Theproduct was placed in a tray and dried at C., ignited at 450 C., groundand sized in the usual way.

Example 5 The procedure of Example 4 was followed except that the pH ofthe gel after sulfuric acid addition was brought to 6 instead of 8.

lysts prepared according to Example I, zirconium promoted catalystsprepared according to Examples 2 and 3,

and thorium catalyst prepared according to Examples 4 and 5. In each runconventional vapor phase catalytic operations were followed, that is tosay, a mixture of naphthalene vapor and air were passed at an elevatedreacting a potassium silicate with sulfuric acid at a pH not in excessof 8, precipitating in the gel a major amount of vanadium pentoxide anda minor amount of a promoter consisting of an oxide of a metal selectedfrom the group temperature through a fluidized catalyst zone in a con- 5consisting of aluminum, zirconium, and thorium, drying verter. The rateof flow of the gases as determined by the entlre precipitation mixturewithout washing out any contact time was maintained within theconventional range soluble material, calcmlng, and grindlng to fluidizedcatain which fluidized catalysts are suspended in the flowing lystfineness. vapors to form a fluidized zone. The conditions and the 2. Amethod according to claim 1 in which the metal results obtained areshown in the following table in which is thor1um. the abbreviation NQ isused for naphthoquinone and FAA 3. A method according to claim 1 inwhich the metal for phthalic anhydride. Naphthalene concentration is 1szirconium. expressed conventionally in mol percent, that is to say, 4. Amethod according to claim 2 in which the silicate mols of naphthaleneper 100 mols of air. and acid are reacted at a pH not in excess of 6.

Inlet Yields, lbs/100 Cone. Temp., Contact Naphthalene Naphtha- OatalystMole 0. Time, lene Percent Sec.

N. Q. P. A. A.

Altos-V405 1.1 300 a 23-25 45-55 31-43 Ah05Vto5 1. 1 200 11 -25 50-0028-41 AhOs-VzOt-.- 2.0 305 11 20-25 50-00 28-41 AlzOs-VzOs- 1. 3 315 820-23 554311 26-36 Ahoy-V505. 1. 7 310 11 20-22 55-55 20-30 zr-oz'wtotNeutral 110 320 12 -33 45 50 2242 PH 6 2. 0 330 12 25-33 45-50 22-42nor-v40, Neutral- 1. 0 300 8 20-20 45-55 31-44 ized to pH 8 1. 0 200 1120-25 50-00 28-40 ThO;-V2O5 Neutralized to H 1.0 310 8 23-25 50-50 28-381.0 330 3 25-34 45-50 21-42 The data on yields in the above tableresults of a number of runs under the conditions as given. in alaboratory converter and some in a converter This application is acontinuation-in-part of the appliare given in the form of rangesrepresenting the Some of the runs were made of pilot plant capacity.

5. A method according to claim 3 in which the silicate and acid arereacted at a pH not in excess of 6.

6. A catalyst prepared by the process of claim 1.

7. A catalyst prepared by the process of claim 2.

8. A catalyst prepared by the process of claim 3.

References Cited in the file of this patent UNITED STATES PATENTS BatesMar. 5, Hale Feb. 18, Fugate et a1. Dec. 28,

1. A METHOD OF PREPARING A CATALYST FOR THE FLUIDIZED CATALYST OXIDATIONOF ORGANIC COMPOUNDS WHICH COMPRISES REACTING A POTASSIUM SILICATE WITHSULFURIC ACID AT A PH NOT IN EXCESS OF 8, PRECIPATING IN THE GEL A MAJORAMOUNT OF VANADIUM PENTOXIDE AND A MINOR AMOUNT OF A PROMOTER CONSISTINGOF AN OXIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMIUM,ZIRCONIUM, AND THORIUM, DRYING THE ENTIRE PRECIPITATION MIXTURE WITHOUTWASHING OUT ANY SOLUBLE MATERIAL, CALCINING, AND GRINDING TO FLUIDIZEDCATALYST FINENESS.